问题 填空题
当半径为1的圆周十二等分,从分点i到分点i+1的向量依次记作
titi+1
,则
t1t2
t2t3
+
t2t3
t3t4
+…+
t12t1
t1t2
=______.
答案

∵把圆分成12份,

∴每一份所对应的圆心角是30度,

连接相邻的两点组成等腰三角形底边平方为2-

3

每对向量的数量积为

3
(2-
3
)
1
2

∴最后结果为12(

3
-
3
2
)=12
3
-18

故答案为:12

3
-18

填空题


A Sports体育运动
Many animals engage in play,but homo sapiens is the only animal (1) have invented sports.Since sports are an invention,a part of culture (2) than an aspect of nature,all definitions of sports are somewhat arbitrary. (3) sports are a human universal found in every known culture or a (4) unique to modern society depends upon one’s definition of sports.Men and (5) have always run,jumped,climbed,lifted,thrown, and wrestled,but they have (6) always performed these physical activities competitively. Although all literate societies seem to (7) contests of one sort or another in which men, and sometimes women, (8) in displays and tests of physical skill and prowess,sports may be (9) defined as physical contests performed for their own sake and not for (10) ulterior end.According to this strict definition,neither Neolithic hunters nor contestants (11) religious ceremonies such as the ancient Olympic Games were engaged in sports. (12) on the stipulation that sports must be performed for their own sake (13) the paradoxical elimination of many activities which are usually thought of as (14) ,such as exercises done for the sake of cardiovascular fitness,races run (15) satisfy a physical education requirement,ball games played to earn a paycheck. (16) definition also means abandonment of the traditional usage in which"sport,"derived (17) Middle English disporter,refers to any light hearted recreational activity.In the. (18) of some 18th- century aristocrats,a game of backgammon and the seduction of (19) milkmaid were both considered good sport,but this usage of the term (20) become archaic.

问答题 简答题